The present invention relates to the field of artificial satellites and more particularly to the field of solar array support structures for external mounting on such satellites.
It is well known in the artificial satellite art that electronic systems in the satellite are powered through the use of solar cells disposed in arrays on flat panels which are oriented so that the solar cells collect solar radiation. As the versatility and power requirements of satellites have increased, the solar array area has increased correspondingly. For example, the SATCOM-I satellite has a solar array area of about 75 square feet. Current solar power systems, such as those used on the SATCOM family of satellites employ solar arrays in the form of a plurality of flat panels which are hinged together and folded accordian style for stowing during launch. The array is unfolded in orbit to extend to its fully size. Such structures provide solar arrays of sufficient size to meet current power requirements and are sufficiently stiff that there is not significant interaction between the attitude control system and the array structure.
Direct broadcast satellites which are now being designed will require much larger solar arrays to meet their power requirements. Such arrays are hundreds of square feet in area and require a several fold increase in the number of folding panels in order to be stowable in the launch vehicle. This means adding hinges and increasing the span of the deployed array, which lowers the natural frequencies of the panel structure even when the latest light weight materials are used. These natural frequencies may be low enough that significant coupling between the satellite attitude control system and the array structure can result.
Such undesired coupling can lead to satellite instability and/or excessive motion of the solar arrays relative to the satellite during attitude changes and corrections. More complicated control of attitude adjustment procedures and the expenditure of increased amounts of attitude control propellant will be required to control such motion even if instability does not result. Such increased propellant expenditure shortens the useful life of a satellite by reducing the time during which the satellite may be maintained on station in a proper attitude.
A solar array structure for a satellite is needed which is stowable for launching and has sufficient stiffness when deployed to prevent undesired interactions between the attitude control system and the solar array support structure even when the array total area is on the order of hundreds of square feet.